Question

1) resolva os sistemas pelo método da substituição

{x-y=5
{x+y=7

Answer 1

$\left \{ {{x-y=5} \atop {x+y=2}} \right. ===> \left \{ {{x=5+y} \atop {x+y=2}} \right. ===> 5+ y+y=2 ===>2y=2-5 ===> 2y=-3 ===> y= -\frac{3}{2} ===> substituindo: x-y=5 ===> - \frac{3}{2}-y=5 ===>-y=5+ \frac{3}{2} ===> -y= -\frac{13}{2} ===> y= \frac{13}{2} ===> y=6 \frac{1}{2}$